（三）Weather Map

A weather map is an important tool for geographers. A succession of three or four maps presents a continuous picture of weather changes. Weather forecasts are able to determine the speed of air masses and fronts; to determine whether an individual pressure area is deepening or becoming shallow and whether a front is increasing or decreasing in intensity. They are also able to determine whether an air mass is retaining its original characteristics or taking on those of the surface over which it is moving. Thus, a most significant function of the map is to reveal a synoptic picture of conditions in the atmosphere at a given time.

All students of geography should be able to interpret a weather map accurately. Weather maps contain an enormous amount of information about weather conditions existing at the time of observation over a large geographical area. They reveal in a few minutes what otherwise would take hours to describe. The United States Weather Bureau issues information about approaching storms, floods, frosts, droughts, and all climatic conditions in general. Twice a month it issues a 30-day "outlook" which is a rough guide to weather conditions likely to occur over broad areas of the United States. These 30-day outlooks are based upon an analysis of the upper air levels which often set the stage for the development of air masses, fronts, and storms.

Considerable effort is being exerted today to achieve more accurate weather predictions. With the use of electronic instruments and earth satellites, enormous gains have taken place recently in identifying and tracking storms over regions which have but few meteorological stations. Extensive experiments are also in progress for weather modification studies. But the limitations of weather modification have prevented meteorological results except in the seeding of super-cooled, upslope mountainous winds which have produced additional orographic precipitation on the windward side of mountain ranges. Nevertheless, they have provided a clearer understanding of the fundamentals of weather elements.

［词汇提示］

geographer n. 地理学者

air mass n. 气团

synoptic adj. 概要的，天气的

weather bureau n. 气象局

meteorological station n. 气象站

orographical adj. 山岳形态的，地形的

barometric adj. 大气压力的

1. One characteristic of weather maps not mentioned by the author in this passage is________.

A. wind speed

B. thermal changes

C. fronts

D. barometric pressure

2. The thirty-day forecast is determined by examining________.

A. upper air levels

B. satellite reports

C. changing fronts

D. daily air maps

3. The observation of weather conditions by satellites is advantageous because it________.

A. gives the scientist information not obtained readily otherwise

B. enables man to alter the weather

C. uses electronic instruments

D. is modern

4. A weather map is synoptic because it________.

A. summarizes a great deal of information

B. can be interpreted accurately

C. appears daily

D. shows changing fronts

5. At the present time, experiments are being conducted in________.

A. 30-day "outlook"

B. controlling storms

C. satellites

D. manipulating weather

［答案解析］

1．B。［解析］三正一误细节考查题。选项A、C和D都在原文中有所提及，只有B项作者未提到，故答案为B。

2．A。［解析］细节考查题。答案在原文第二段最后一句话：These 30-day outlooks are based upon an analysis of the upper air levels which often set the stage for the development of air masses, fronts, and storms.

3．D。［解析］涉及原因的细节考查题。文中未提到选项A和B，而选项C和卫星的共同使用使得天气预报更为精确。

4．A。［解析］涉及原因的细节考查题。此处synoptic意为“概要的”，那么答案就显而易见了，“气象图是展示整体概况的，因为它概述了大量的信息”。

5．D。［解析］细节考查题。答案在原文最后一段第三句：Extensive experiments are also in progress for weather modification studies. 故答案为D。选项A、B和C都属于以偏概全的局部信息。